Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased charge cooling due to its increased heat of vaporization compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. Further, water may be included in the mixture. The above approaches purport to improve engine fuel economy and increase utilization of renewable fuels.
The inventors herein have recognized several issues with such an approach. Specifically, local availability and cost of various fuels can affect the type of fuel and/or water content, if any, supplied to the vehicle. As such, to take advantage of local availability and cost structures, the customer may use a range of alcohol/water/hydrocarbon ratios for the engine to utilize. However, the composition of the fuel may not only affect its knock suppression capability, but may also affect its tendency toward pre-ignition, as well as the flame speed of the overall air-fuel mixture. In other words, engine power and fuel economy may be compromised due to the effect of the variation in alcohol/water/hydrocarbon ratios of the knock suppression fluid.
As such, in one approach, a system for an engine is provided. The system comprises a cylinder located in the engine; a delivery system configured to deliver fuel and a fluid to at least an engine cylinder while the vehicle is traveling on the road, said fluid including at least some water; and a controller for varying an amount of said fuel and fluid delivered to the cylinder in different ratios as a condition varies, said controller further varying a spark timing of a spark in said cylinder as an amount of water in said fluid varies.
In this way, it is possible to adjust spark timing to accommodate variation in water delivered to the engine, thereby enabling more advantage of knock suppression while reducing likelihood of pre-ignition. For example, in the example where 100% ethanol is used in a secondary injection for knock suppression, engine operation near the spark knock limit may initiate pre-ignition under some conditions. Whereas when using knock suppression injection with a higher water content, pre-ignition may be much less likely near the spark knock limit. Thus by using the composition of the knock suppression fuel in the control system, it is possible to adjust ignition timing to take advantage of current conditions, as well as to accommodate variation in water content.